Web Services Coordination(WS-Coordination) 1.1

Web Services Coordination(WS-Coordination) 1.1

Committee Specification, 04 December 2006

Document Identifier:

wstx-wscoor-1.1-spec-cs-01

Location:

Technical Committee:

OASIS WS-TX TC

Chair(s):

Eric Newcomer, Iona

Ian Robinson, IBM

Editor(s):

Max Feingold, Microsoft

Ram Jeyaraman, Microsoft

Abstract:

This specification (WS-Coordination) describes an extensible framework for providing protocols that coordinate the actions of distributed applications. Such coordination protocols are used to support a number of applications, including those that need to reach consistent agreement on the outcome of distributed activities.

The framework defined in this specification enables an application service to create a context needed to propagate an activity to other services and to register for coordination protocols. The framework enables existing transaction processing, workflow, and other systems for coordination to hide their proprietary protocols and to operate in a heterogeneous environment.

Additionally this specification describes a definition of the structure of context and the requirements for propagating context between cooperating services.

Status:

This document was last revised or approved by the WS-TX TC on the above date. The level of approval is also listed above. Check the current location noted above for possible later revisions of this document. This document is updated periodically on no particular schedule.

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Table of Contents

1Introduction

1.1 Model

1.2 Composable Architecture

1.3 Extensibility

1.4 Terminology

1.5 Namespace

1.6 XSD and WSDL Files

1.7 Coordination Protocol Elements

1.8 Normative References

1.9 Non-normative References

2Coordination Context

3Coordination Service

3.1 Activation Service

3.1.1 CreateCoordinationContext

3.1.2 CreateCoordinationContextResponse

3.2 Registration Service

3.2.1 Register Message

3.2.2 RegistrationResponse Message

4Coordination Faults

4.1 Invalid State

4.2 Invalid Protocol

4.3 Invalid Parameters

4.4 Cannot Create Context

4.5 Cannot Register Participant

5Security Model

5.1 CoordinationContext Creation

5.2 Registration Rights Delegation

6Security Considerations

7Use of WS-Addressing Headers

8Glossary

Appendix A. Acknowledgements

wstx-wscoor-1.1-spec-cs-0104 December 2006

1Introduction

The current set of Web service specifications (SOAP [SOAP 1.1][SOAP 1.2]and WSDL [WSDL]) defines protocols for Web service interoperability. Web services increasingly tie together a large number of participants forming large distributed computational units – we refer to these computation units as activities.

The resulting activities are often complex in structure, with complex relationships between their participants. The execution of such activities often takes a long time to complete due to business latencies and user interactions.

This specification defines an extensible framework for coordinating activities using a coordinator and set of coordination protocols. This framework enables participants to reach consistent agreement on the outcome of distributed activities. The coordination protocols that can be defined in this framework can accommodate a wide variety of activities, including protocols for simple short-lived operations and protocols for complex long-lived business activities. For example, WS-AtomicTransaction [WSAT] and WS-BusinessActivity [WSBA]specifications use and build upon this specification.

Note that the use of the coordination framework is not restricted to transaction processing systems; a wide variety of protocols can be defined for distributed applications.

1.1Model

This specification describes a framework for a coordination service (or coordinator) which consists of these component services:

An Activation service with an operation that enables an application to create a coordination instance or context.

A Registration service with an operation that enables an application to register for coordination protocols.

A coordination type-specific set of coordination protocols.

This is illustrated below in Figure 1.

Applications use the Activation service to create the coordination context for an activity. Once a coordination context is acquired by an application, it is then sent by whatever appropriate means to another application.

The context contains the necessary information to register into the activity specifying the coordination behavior that the application will follow.

Additionally, an application that receives a coordination context may use the Registration service of the original application or may use one that is specified by an interposing, trusted coordinator. In this manner an arbitrary collection of Web services may coordinate their joint operation.

1.2Composable Architecture

By using the SOAP [SOAP 1.1][SOAP 1.2]and WSDL [WSDL] extensibility model, SOAP-based and WSDL-based specifications are designed to be composed with each other to define a rich Web services environment. As such, WS-Coordination by itself does not define all the features required for a complete solution. WS-Coordination is a building block that is used in conjunction with other specifications and application-specific protocols to accommodate a wide variety of protocols related to the operation of distributed Web services.

The Web service protocols defined in this specification should be used when interoperability is needed across vendor implementations, trust domains, etc. Thus, the Web service protocols defined in this specification can be combined with proprietary protocols within the same application.

1.3Extensibility

The specification provides for extensibility and flexibility along two dimensions. The framework allows for:

The publication of new coordination protocols.
The selection of a protocol from a coordination type and the definition of extension elements that can be added to protocols and message flows.

Extension elements can be used to exchange application-specific data on top of message flows already defined in this specification. This addresses the need to exchange such data as transaction isolationlevels or other information related to business-level coordination protocols. The data can be logged for auditing purposes, or evaluated to ensure that a decision meets certain business-specific constraints.

To understand the syntax used in this specification, the readershould be familiar with the WSDL[WSDL] specification, including its HTTP and SOAP binding styles. All WSDL port type definitions provided here assume the existence of corresponding SOAP and HTTP bindings.

Terms introduced in this specification are explained in the body of the specification and summarized in the glossary.

1.4Terminology

The uppercase key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].

This specification uses an informal syntax to describe the XML [XML]grammar of the XML fragments below:

The syntax appears as an XML instance, but the values indicate the data types instead of values.
Element names ending in "..." (such as <element.../> or <element...>) indicate that elements/attributes irrelevant to the context are being omitted.
Attributed names ending in "..." (such as name=...) indicate that the values are specified below.
Grammar in bold has not been introduced earlier in the document, or is of particular interest in an example.
<-- description --> is a placeholder for elements from some "other" namespace (like ##other in XSD).
Characters are appended to elements, attributes, and  as follows: "?" (0 or 1), "*" (0 or more), "+" (1 or more). The characters "[" and "]" are used to indicate that contained items are to be treated as a group with respect to the "?", "*", or "+" characters.
The XML namespace prefixes (defined below) are used to indicate the namespace of the element being defined.
Examples starting with <?xml contain enough information to conform to this specification; others examples are fragments and require additional information to be specified in order to conform.

XSD schemas and WSDL definitions are provided as a formal definition of grammars [XML-Schema1][XML-Schema2][WSDL].

1.5Namespace

The XML namespace [XML-ns] URI that MUST be used by implementations of this specification is:

The namespace prefix "wscoor" used in this specification is associated with this URI.

The following namespaces are used in this document:

Prefix / Namespace
S11 /
S12 /
wscoor /
wsa /

1.6XSD and WSDL Files

The XML schema and the WSDL declarations defined in this document can be found at the following locations:

SOAP bindings for the WSDL documents defined in this specification MUST use "document" for the style attribute.

1.7Coordination Protocol Elements

The protocol elements define various extensibility points that allow other child or attribute content. Additional children and/or attributes MAY be added at the indicated extension points but MUST NOT contradict the semantics of the parent and/or owner, respectively. If a receiver does not recognize an extension, the receiver SHOULD ignore the extension.

1.8Normative References

[RFC2119]S. Bradner, “Key words for use in RFCs to Indicate Requirement Levels”, IETF RFC 2119, March 1997.

[SOAP 1.1]W3C Note, "SOAP: Simple Object Access Protocol 1.1," 08 May 2000.

[SOAP 1.2]W3C Recommendation, "SOAP Version 1.2 Part 1: Messaging Framework", June 2003.

[XML]W3C Recommendation, "Extensible Markup Language (XML) 1.0 (Fourth Edition)," 16August2006.

[XML-ns]W3C Recommendation, "Namespaces in XML 1.0 (Second Edition)," 16August2006.

[XML-Schema1]W3C Recommendation, "XML Schema Part 1: Structures Second Edition," 28October 2004.

[XML-Schema2]W3C Recommendation, "XML Schema Part 2: Datatypes Second Edition," 28October 2004.

[WSADDR]Web Services Addressing (WS-Addressing) 1.0, W3C Recommendation,

[WSDL]Web Services Description Language (WSDL) 1.1

[WSPOLICY]Web Services Policy Framework (WS-Policy), VeriSign, Microsoft, Sonic Software, IBM, BEA Systems, SAP, September 2004.

[WSSec]OASIS Standard 200401, March 2004, "Web Services Security: SOAP Message Security 1.0 (WS-Security 2004)",

[WSSecPolicy]Web Services Security Policy Language (WS-SecurityPolicy), Microsoft, VeriSign, IBM, and RSA Security Inc., July 2005.

[WSSecConv]Web Services Secure Conversation Language (WS-SecureConversation), OpenNetwork, Layer7, Netegrity, Microsoft, Reactivity, IBM, VeriSign, BEA Systems, Oblix, RSA Security, Ping Identity, Westbridge, Computer Associates, February 2005.

[WSTrust]Web Services Trust Language (WS-Trust), OpenNetwork, Layer7, Netegrity, Microsoft, Reactivity, VeriSign, IBM, BEA Systems, Oblix, RSA Security, Ping Identity, Westbridge, Computer Associates, February 2005.

1.9Non-normative References

[WSAT]Web Services Atomic Transaction (WS-AtomicTransaction)

[WSBA]Web Services Business Activity (WS-BusinessActivity)

2Coordination Context

The CoordinationContext is used by applications to pass Coordination information to parties involved in an activity. CoordinationContext elements are propagated to parties which may need to register Participants for the activity. Context propagation may be accomplished using application-defined mechanisms --e.g. as a header element of a SOAP application message sent to such parties. (Conveying a context in an application message is commonly referred to as flowing the context.) A CoordinationContext provides access to a coordination registration service, a coordination type, and relevant extensions.

The following is an example of a CoordinationContext supporting a transaction service:

<?xml version="1.0" encoding="utf-8"?>

S11:Envelope xmlns:S11="

S11:Header>

. . .
<wscoor:CoordinationContext

xmlns:wsa="

xmlns:wscoor="

xmlns:myApp="

S11:mustUnderstand="true">

<wscoor:Identifier>

</wscoor:Identifier>

<wscoor:Expires>3000</wscoor:Expires>

<wscoor:CoordinationType>

</wscoor:CoordinationType>

<wscoor:RegistrationService>

<wsa:Address>

</wsa:Address>

<wsa:ReferenceParameters

<myApp:BetaMark> ... </myApp:BetaMark>

<myApp:EBDCode> ... </myApp:EBDCode>

</wsa:ReferenceParameters

</wscoor:RegistrationService>

<myApp:IsolationLevel>

RepeatableRead

</myApp:IsolationLevel>

</wscoor:CoordinationContext>

. . .

</S11:Header>

</S11:Body>

. . .

</S11:Body >

</S11:Envelope>

When an application propagates an activity using a coordination service, applications MUST include a CoordinationContext in the message.

When a context is exchanged as a SOAP header, the mustUnderstand attribute MUST be present and its value MUSTbe true.

3Coordination Service

The Coordination service (or coordinator) is an aggregation of the following services:

Activation service: Defines a CreateCoordinationContext operation that allows a CoordinationContext to be created. The exact semantics are defined in the specification that defines the coordination type. The Coordination service MAY support the Activation service.
Registration service: Defines a Register operation that allows a Web service to register to participate in a coordination protocol. The Coordination service MUST support the Registration service.
A set of coordination protocol services for each supported coordination type. These are defined in the specification that defines the coordination type.

Figure 2 illustrates an example of how two application services (App1 and App2) with their own coordinators (CoordinatorA and CoordinatorB) interact as the activity propagates between them. The protocol Y and services Ya and Yb are specific to a coordination type, which are not defined in this specification.

App1 sends a CreateCoordinationContext for coordination type Q, getting back a Context Ca that contains the activity identifier A1, the coordination type Q and an Endpoint Reference to CoordinatorA's Registration service RSa.
App1 then sends an application message to App2 containing the Context Ca.
App2 prefers to use CoordinatorB instead of CoordinatorA, so it uses CreateCoordinationContext with Ca as an input to interpose CoordinatorB. CoordinatorB creates its own CoordinationContext Cb that contains the same activity identifier and coordination type as Ca but with its own Registration service RSb.
App2 determines the coordination protocols supported by the coordination type Q and then Registers for a coordination protocol Y at CoordinatorB, exchanging Endpoint References for App2 and the protocol service Yb. This forms a logical connection between these Endpoint References that the protocol Y can use.
This registration causes CoordinatorB to decide to immediately forward the registration onto CoordinatorA's Registration service RSa, exchanging Endpoint References for Yb and the protocol service Ya. This forms a logical connection between these Endpoint References that the protocol Y can use.

Figure 2: Two applications with their own coordinators

It should be noted that in this example several actions are taken that are not required by this specification, but which may be defined by the coordination type specification or are implementation or configuration choices. Specifications of coordination types and coordination protocols that need to constrain the sub-coordination behavior of implementations SHOULDstate these requirements in their specification.

3.1Activation Service

The Activation service creates a new activity and returns its coordination context.

An application sends:

CreateCoordinationContext

The structure and semantics of this message aredefined in Section 3.1.1.